This invention relates to injecting a delayed and moderated self-foaming aqueous liquid into preferentially permeable pores or other openings in or along a reservoir formation to temporarily fill or plug those openings with a relatively immobile foam.
The temporary filling or plugging of such openings with foam is a known procedure. Numerous ways for conducting and utilizing such a process are described in patents such as the following: U.S. Pat. No. 3,273,643 describes sequentially adding foaming surfactants and gas-generating reactants to "drowned" wells to initiate an in situ foam generation which displaces liquid and reduces the hydrostatic pressure. U.S. Pat. No. 3,299,953 describes injecting foam or alternating slugs of gas and aqueous surfactant into a mud-filled annulus around a pipe string being cemented into a wellbore to both displace the mud and temporarily plug the openings within the adjacent earth formations. U.S. Pat. No. 3,612,179 describes a reservoir acidization in which a sequency of acid, surfactant, gas, and acid, is injected so that foam temporarily plugs the most permeable portions and diverts the acid into less permeable portions of the reservoir. U.S Pat. No. 3,893,511 describes a process for producing oil from a reservoir having a dual permeability system by injecting alternating slugs of surfactant and gas, so that foam plugs the most permeable openings and diverts gas into less permeable openings, with the oil being recovered during a backflow production operation. And, U.S. Pat. No. 4,130,165 describes a process for reducing water coning by injecting a slug of gas followed by a slug of oil containing an emulsifier, then backflowing, in order to form an emulsion or foam that plugs zones from which water is produced.
Particularly useful gas-generating aqueous liquid solutions are described in a copending Patent Application Ser. No. 902,636 filed May 4, 1978, by E. A. Richardson and R. F. Scheuerman, which relates to reducing hydrostatic pressure within a liquid-containing wellbore. The 902,636 application describes injecting a solution of nitrogen gas-forming reactants with the composition and concentration of the solution being correlated with the pressure, temperature and volume properties of the well and reservoir so that the solution remains substantially unreactive until it reaches a selected depth within the borehole and then generates gas at a moderately rapid rate. Patent Application Ser. No. 28,025 filed Apr. 6, 1979, by E. A. Richardson, R. F. Scheuerman and D. C. Berkshire relates to chemically inducing a backsurge of fluid through well casing perforations. The 28,025 application describes injecting a solution of nitrogen gas-forming reactants through the well casing perforations and into the reservoir. It uses a backsurge-inducing solution which comprises the solution of the 902,636 application modified by adding a reaction-retarding alkaline buffer and a pH-reducing reactant capable of subsequently overriding that buffer. The composition is ranged so that the solution remains substantially unreactive within the well but, within the reservoir, becomes an acidic, fast-reacting solution which generates a rapid-rising pulse of heat and gas that causes a debris-removing backsurging of fluids through the casing perforations. The disclosures of the 902,636 and 28,025 applications are incorporated herein by cross reference.